Grit

6 words can not accurately describe grit. It is not a superficial adjective intended for daily use. Grit is deep, not easily defined and a person can have grit in some areas of their life but not others.

You must have a personal connection with the task to access grit. That personal connection helps define your "why". That "why" is what gives you the endurance to continue on your chosen path. It could be as simple as self betterment or as complex as a relationship.

In the military grit may be the number one deciding factor. It is your will to live vs theirs.
We get better in order to end the battle before we need to worry about friendly grit.